1. Field of the Invention
The present invention relates generally to a disk drive and, in particular, to a head positioning control technique including a position correction relating to an offset between a read head and a write head.
2. Description of the Related Art
Generally, in a disk drive represented by a hard disk drive, a composite type head unit is used in which a read head and write head are separately mounted on the same slider.
The read head is comprised of, usually, an MR (magnetoresistive) element or GMR (giant magnetoresistive) element and performs a read operation (data read operation). The write head is usually comprised of an inductive thin-film head element and performs a write operation (data write operation).
These heads are usually mounted on a rotary (rotation) type actuator. The actuator is rotationally driven in a radial direction over a disk medium by a driving force of a voice coil motor (VCM) to allow the head to be positioned to a target position (target track or target cylinder).
Where the head is positioned over the disk medium by the rotary type actuator, since the read head and write head are separated, there is a gap spacing (Grw) in the peripheral direction and, further, an offset occurs between the read head and the write head due to their different radial positions over the disk medium.
Stated in more detail, when, at a data read operation time, the read head is positioned relative to a data position (track position) to which recording is made by the write head, it is necessary to effect a position correction corresponding to the offset. In the prior art technique, a positioning system is proposed in which, by applying a calculated offset amount, the read head is set to a data position for tracking over a disk medium (see JPN PAT APPLN KOKAI PUBLICATION NO. 2001-134905).
In the disk drive, on the other hand, it is known that, where any external impact is applied during an operation or any disk medium is incorporated in which servo data is recorded by an external servo track writer, a disk runout occurs in synchronism with the rotation of a spindle motor (SPM) for spinning the disk medium.
If such disk runout occurs, the positional accuracy is lowered when the head position control is performed and in order to deal with this problem an improved technique is disclosed, for example, in JPN PAT APPLN KOKAI PUBLICATION NO. 11-126444.
In the disk drive head positioning control set out above as the prior art technique, consideration is given to the offset between the read head and the write head and an improved system is proposed for improving the positional accuracy relating to the disk runout.
With respect to the head positioning control system capable of coping with any variation in offset resulting from the disk runout, however, no proposal has been disclosed in the prior art technique. Therefore, if any disk runout occurs, it is not possible to, in the head positioning control by the conventional offset correction, set the head to a target position for proper tracking on the disk medium. This may present a lowered positional accuracy problem.